Soil degradation by metal and metalloid (metal[loid]) contamination represents a widespread environmental threat. Most studies investigating soil metal(loid) contamination have disregarded the soil quality concept. Enzyme activities (EAs) are good soil quality indicators due to their direct connection to functions related to C, N, P, and S cycles and their sensitivity to metal(loid) contamination. This review (a) provides an overview of the development of soil quality indices (SQIs) based on EAs in metal(loid) contaminated soils, and (b) evaluates the effects of individual metal(loid)s and their combinations on the activities of the most common enzymes involved in the C, N, P, and S cycles. Four intracellular mechanisms dominate the inhibition of EAs by metal(loid)s: (a) transcription inhibition, (b) protein denaturation, (c) cell division inhibition, (d) cell membrane disruption. These mechanisms can also be further exacerbated in soil by nonspecific exoenzyme inhibition. The main EAs used as indicators for metal(loid) contaminated soils are dehydrogenase (DHA), arylsulfatase (ARY), urease (UA), acid phosphatase (Pacid), alkaline phosphatase (Palk), and catalase (CAT). These enzymes are sensitive to metal(loid) contamination, with DHA and ARY being the most sensitive indicators (62 and 56% inhibition, respectively, when averaged over all metal[loid] contamination levels). Other enzymes are inhibited by 32% (UA), 23% (Palk), 18% (Pacid), and 18% (CAT). We suggest principles for the development of SQIs considering biotic soil functions via the use of EAs. This review is the first presenting SQIs based on EAs for metal(loid) contaminated soils, and represents the first quantitative analysis of metal(loid) effects on EAs.

中文翻译：

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金属（类）污染的土壤质量指数：酶学观点

金属和准金属（金属）污染对土壤的降解代表了广泛的环境威胁。大多数研究土壤金属（金属）污染的研究都忽略了土壤质量的概念。酶活（EAs）是与土壤C，N，P和S循环相关的功能直接相关，并且对金属（金属）污染敏感，因此是良好的土壤质量指标。这篇综述（a）概述了基于EAs在被金属（胶体）污染的土壤中的土壤质量指数（SQI）的发展，并且（b）评估了单个金属（胶体）及其组合对土壤质量活动的影响参与C，N，P和S循环的最常见酶。四种细胞内机制主导着金属（金属）对EA的抑制作用：（a）转录抑制，（b）蛋白质变性，（c）细胞分裂抑制，（d）细胞膜破坏。这些机制还可以通过非特异性外源酶抑制作用在土壤中进一步加剧。用作金属（金属）污染土壤指示剂的主要EA是脱氢酶（DHA），芳基硫酸酯酶（ARY），脲酶（UA），酸性磷酸酶（Pacid），碱性磷酸酶（Palk）和过氧化氢酶（CAT）。这些酶对金属（金属）污染敏感，其中DHA和ARY是最敏感的指示剂（按所有金属（金属）污染水平的平均值分别抑制62％和56％）。其他酶被32％（UA），23％（Palk），18％（Pacid）和18％（CAT）抑制。我们建议通过使用EA来考虑生物土壤功能的SQI的开发原则。这篇评论是首次提出基于EA的SQI，用于污染金属（胶体）的土壤，